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|United States Patent
,   et al.
May 28, 1996
System and method of removing contaminants from solid surfaces and
A method and system for removing a surface layer contaminated with
radioactive and/or hazardous material and subsequently treating the waste
to remove contaminants and provide an essentially contaminant-free final
effluent. The contaminated material is removed by blasting the surface
with a pressurized stream of air and sodium bicarbonate abrasive media,
and the media is dissolved in water subsequent to the blasing operation.
The resulting waste is treated in a sequence of steps including adjustment
of pH, aeration and separation into primarily solid and liquid phases by
precipitation of solids, which are removed for appropriate disposal. The
primarily liquid phase is successively passed through a particle filter, a
granulated activated carbon filter and a polishing unit to produce the
clean final effluent.
Brown; Terry L. (Fayetteville, NY);
Geiss; Anthony J. (Liverpool, NY);
Grieco; Scott (Skaneateles, NY);
Neubauer; Eric D. (East Syracuse, NY);
Rhea; James R. (Baldwinsville, NY)
O'Brien & Gere Technical Services, Inc. (Syracuse, NY)
February 9, 1995|
|Current U.S. Class:
||451/88; 134/6; 134/7; 134/12; 134/13; 451/38 |
|Field of Search:
U.S. Patent Documents
|3895465||Jul., 1975||Korn et al.||451/88.
|4800063||Jan., 1989||Mierswa et al.||51/321.
|5160547||Nov., 1992||Kirschner et al.||134/7.
|5290364||Mar., 1994||Stein et al.||134/7.
|5302324||Apr., 1994||Morikawa et al.||252/626.
|5316587||May., 1994||Yam et al.||51/304.
|5322644||Jun., 1994||Dunn et al.||252/626.
Primary Examiner: Kisliuk; Bruce M.
Assistant Examiner: Morgan; Eileen P.
Attorney, Agent or Firm: McGuire; Charles S.
Parent Case Text
This is a divisional application of Ser. No. 08/272,054, filed Jul. 8, 1994
now U.S. Pat. No. 5,457,261.
What is claimed is:
1. A system for removing toxic and/or radioactive contaminants from the
surface of steel, concrete, or the like, and treating the waste generated
by such removal in a manner resulting in a volume of contaminated solids
which is significantly reduced from prior art decontamination systems and
an essentially contaminant-free final effluent, said system comprising:
a) first means for directing a stream of sodium-bicarbonate based abrasive
blasting media onto said surface at a velocity sufficient to remove a thin
layer of material including said contaminants from said surface;
b) second means for contacting said media with a quantity of water
sufficient to dissolve substantially all of said media;
c) third means for adjusting the pH of a first mixture, consisting
essentially of said water, dissolved media and material removed from said
surface, to a first value at which substantially all carbonates are in the
form of carbon dioxide gas and water;
d) fourth means for removing said carbon dioxide gas from said first
mixture to form a remaining, second mixture;
e) fifth means for adjusting the pH of said second mixture to a second
value conducive to precipitation of solids, including substantially all of
said contaminants, from said second mixture; and
f) sixth means for separating said second mixture into primarily liquid and
2. The system of claim 1 wherein said first value is not greater than about
3. The system of claim 1 wherein said first means comprises a blasting
nozzle having an internal chamber, an outlet and means for introducing
pressurized air and said blasting media into said chamber for emission of
a pressurized stream of said media from said outlet.
4. The system of claim 3 wherein said second means comprises means for
directing at least a portion of said quantity of water onto said surface.
5. The system of claim 4 wherein said third means comprises means for
adding an appropriate acid to said first mixture.
6. The system of claim 5 wherein said acid is sulfuric acid.
7. The system of claim 5 wherein said fourth means comprises means for
aerating said first mixture to blow off said carbon dioxide gas.
8. The system of claim 7 wherein said fifth means comprises means for
adding an appropriate caustic material to said second mixture.
9. The system of claim 8 wherein said sixth means comprises means for
adding appropriate coagulating and/or flocculating agents to said second
10. The system of claim 8 wherein said sixth means comprises a clarifier.
11. The system of claim 10 and further including means for further
de-watering said primarily solid phase after removal from said clarifier.
12. The system of claim 10 and further including particle filter means for
filtering particulates from said primarily liquid phase after removal from
13. The system of claim 12 and further including GAC filter means for
absorption of organic contaminants from said primarily liquid phase.
14. The system of claim 13 and further including a polishing unit through
which said primarily liquid phase is passed to provide an essentially
15. The system of claim 14 and further including means for adjusting the pH
of said final effluent.
BACKGROUND OF THE INVENTION
The present invention relates to systems and methods for removing
radioactive and/or hazardous materials from steel, concrete, or other
solid surfaces and thereafter treating the generated waste to render a
significant portion thereof essentially free of contaminants, and
disposing of the reduced volume of contaminated waste. More specifically,
the invention relates to systems and methods wherein a pressurized mixture
of sodium bicarbonate and air is ejected from a nozzle and directed in a
concentrated spray upon a contaminated surface, with water being added at
the nozzle during blasting as required to control dust. Water is added
after the blasting to dissolve the spent sodium bicarbonate, and the waste
material is treated to remove a significant portion of the contaminated
solids, the resulting liquid phase being further treated for removal of
contaminants to produce an essentially contaminant-free final effluent.
Various surfaces which are contacted by radioactive, toxic and/or other
hazardous materials within industrial facilities, and the like, must
periodically be decontaminated in order to permit inspection and/or
repair, as well as reuse, recycling or sale of the building or equipment
incorporating such surfaces. Among the more common procedures employed to
effect such decontamination is that of abrasive blasting. Abrasive media
used for surface decontamination have included sand, black beauty (coal
slag) and steel shot, as well as liquid or solid carbon dioxide. The use
of materials which remain in a solid state after impinging upon and
removing contaminants from the treated surface requires costly handling
and disposal of a large volume of contaminated waste. Media which is in,
or converts to, the gaseous state is difficult to contain and
It is a principal object of the present invention to provide a method and
system employing a number of otherwise conventional elements of apparatus
in novel sequence and combination to effect significant reduction in the
volume of contaminated solid waste generated in decontamination of solid
surfaces by abrasive blasting.
Another object is to provide a novel and improved method and system of
removing radioactive or hazardous material from a solid surface by
abrasive blasting which reduces the cost of disposal of contaminated
A further object is to provide a method and system for removal of
contaminants from solid surface by abrasive blasting utilizing water
soluble, low cost, readily available blasting media, namely, sodium
Other objects will in part be obvious and will in part appear hereinafter.
SUMMARY OF THE INVENTION
The decontamination method and system of the invention may be conveniently
separated into two components, namely a blasting and a treatment method
and system. The two components are, of course, related and carried out
successively. The surface which is initially contaminated is contacted by
a high-pressure, air-borne stream of sodium bicarbonate, or a commercial
abrasive blasting medium containing or consisting of sodium bicarbonate. A
water spray may also be directed upon the surface for dust suppression; in
any case, sufficient water is mixed with the resulting waste to dissolve
the sodium bicarbonate following the blasting operation.
Contaminated material is removed from the surface by the spray from the
blast nozzle. When sufficient material has been removed to render the
surface essentially free of contaminants, rinse water is directed upon the
surface to ensure that all contaminated material and spent blast media is
removed. The waste, consisting of the spent abrasive media and water, as
well as the material removed from the surface, is subjected to the
The waste is first collected in an equalization tank where it is mixed with
water to ensure that the sodium bicarbonate is thoroughly dissolved, and
acid is added to adjust the pH to about 5 s.u. The waste then flows to an
aeration tank where it is aerated to liberate carbonate as carbon dioxide
gas. In the next tank, caustic chemicals are added to elevate the pH to a
value adequate for solids precipitation. Chemical coagulants and/or
flocculants are added, if necessary, prior to flow of the treated waste
into a clarification tank for precipitation of contaminated solids. The
precipitated solids, constituting a high percentage of all solids
initially contained in the waste stream, are removed from the
clarification tank and suitably packaged for disposal, after further
reduction of solids volume by additional liquid removal, if desired.
Liquid waste from the tank is passed successively through one or more
particle filters for removal of residual macro-solids, and a granulated
activated carbon (GAC) filter for removal of organic contaminants. The
liquid waste is then subjected to polishing for dissolved radioactive ion
and heavy metal removal. The final effluent is essentially free of all
contaminants and acid may be added to adjust pH prior to recycling or
The foregoing and other features of the invention will be more readily
understood and fully appreciated from the following detailed description,
taken in conjunction with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
The single FIGURE is a diagrammatic representation of the blasting and
treatment system, also illustrating the steps in the method of the
Referring now to the drawings, a surface of concrete, steel, or the like,
is indicated by reference numeral 10. Surface contamination, such as PCBs
and radioactive wastes, must be removed from surface 10 in order that the
building or equipment of which surface 10 is a part may be inspected,
repaired, used, recycled or sold. Decontamination is effected by removal
of material from surface 10 with spray from blasting nozzle 12 directed
upon surface 10.
Pressurized air is supplied to nozzle 12 from compressed air source 14. The
air supply is also connected to media pot 16 via line 18. Pot 16 contains
a supply of sodium bicarbonate-based abrasive blasting media such as that
available from the assignee hereof, as well as other commercial sources.
Such products may include, in addition to relatively coarse sodium
bicarbonate abrasive, flow enhancers and other ingredients. The
pressurized air supplied to pot 16 is at a pressure slightly higher than
the air pressure in nozzle 12 to ensure a supply of blasting media to
nozzle 12 at a desired rate. Suitable pressure regulators, gauges, valves
and controls (not shown) are provided in accordance with conventional
practice. Water is supplied from an appropriate source through line 20 and
mixed with the air-media stream internally or externally of nozzle 16,
which may be of any standard commercial design appropriate to the
described application, for dust suppression during the blasting operation.
Compressed air is preferably delivered to nozzle 12 at a pressure of 80-100
psi and a rate of 250-300 cfm. Media of the aforementioned type is
provided at a rate of 1.0-2.5 pounds per minute. Water usage is in the
range of about 0.3-0.9 gallons per minute. Following blasting with the
air-media-water stream, surface 10 is rinsed with 0.75-1.0 gallons of
water per pound of media used. The aforementioned sodium bicarbonate-based
blasting media is preferred due to its water solubility, relatively low
cost and ready availability.
Waste from the blasting process, including all water, blasting media and
material removed from surface 10, is collected and deposited via line 22
in equalization tank 24, serving to balance flow rates of the waste
between the blasting and treatment operations. If the quantity of water
from the blasting operation is not sufficient to dissolve all of the
sodium bicarbonate media, further water may be added for such purpose in
tank 24. Sulfuric or other appropriate acid is added via line 26 to adjust
the pH of the waste in tank 24 to a value of about 5 s.u. Waste from
equalization tank 24 is deposited in aeration tank 26 where air from
source 14, or from a separate source, is released within the waste to
accelerate liberation of carbon dioxide gas formed from the carbonates in
From aeration tank 26 the waste is deposited in tank 28 where caustic
material is added, as indicated at 30 to elevate the pH to a level
suitable for precipitation of solids from the waste. Depending upon the
nature of the solids in the waste, coagulating and/or flocculating agents
may be added to the waste in one or both of tanks 34 and 36. Such
chemicals are selected for their ability to cause the solids in the waste
to precipitate out of the liquid phase and may not be required in some
applications, e.g., when the solids are largely cement powder. Solid
contaminants are removed from clarifier 38 through line 40 and may be
further de-watered for volume reduction before being containerized for
appropriate disposal in accordance with the nature and level of
The remaining waste, typically having a water content of more than 95%, is
delivered from clarifier 38 through line 42 to particle filters 44. After
passing through particle filters 44, wherein additional contaminated
macro-solids are removed, the waste is passed through a granulated
activated charcoal (GAC) filter 46 which adsorbs organic contaminants.
From GAC 46 the waste is subjected to a polishing operation in unit 48,
such as an ion-exchange column.
Upon exiting polishing unit 48, the liquid effluent is essentially
contaminant-free. Before recycling or other disposition of the final
effluent, it may be desirable to adjust pH by addition of a suitable
acidic solution through line 50 to the final effluent in tank 52. Particle
filters 44 may comprise conventional paper media filter cartridges. GAC
filter 46 and polishing unit 48 are also commercially available items, and
the capacity and other characteristics thereof are chosen in accordance
with the anticipated nature and volume of contaminants to be removed. The
media of particle filters 44 and GAC 46 will, of course, require
replacement from time to time, with proper handling and disposal of spent
Among the advantages of the surface decontamination method and system of
the invention is the low volume of solid contaminants requiring disposal,
as compared to conventional systems. That is, the volume of solid
contaminants removed from clarifier 38 may be not appreciably greater than
the material actually removed from surface 10, whereas it is not unusual
in prior art systems for the volume of contaminated solid waste to exceed
fifty times that of the material removed from the initially contaminated
surface. Final effluent through line 54 is suitable for discharge into
uncontaminated municipal wastes or, if desired, for recycling to the